Method for the production of a starch raw material and a starch milling system

ABSTRACT

The invention is directed to a new method for the production of a starch raw material for subsequently obtaining pure starch from wheat, rye, corn or barley. Fractions of starch which is damaged as little as possible are produced by means of roller grinding and sifting devices. The material is ground repeatedly and sifted with the system of advanced milling, wherein it is suggested in particular to guide the material two to five times via double-grinding stages without sifting between the double grindings. Sifting is effected subsequent to the double grinding. The invention also concerns a starch milling system which comprises two to five double-grinding passes with two grinding-roll pairs which are connected one after the other and are preferably constructed as an eight-roll mill.

This application is a continuation of application Ser. No. 348,484,filed Mar. 22, 1989, now abandoned.

TECHNICAL FIELD

The invention is directed to a method for the production of a starch rawmaterial for subsequently obtaining pure starch from wheat, rye, corn orbarley, wherein fractions of starch which is damaged as little aspossible are produced by means of roll grinding and sifting devices,wherein the material is ground repeatedly and sifted with the system ofadvanced milling, and to a starch milling system for the production ofstarch raw material for subsequently obtaining pure starch.

BACKGROUND ART

The most recent development in starch production was determined by twoessential findings which contributed considerably to economicalproduction. The first finding was that starch kernels which are damagedduring grinding decrease the subsequent yield of pure starch in thestarch factory. If the starch is damaged in the production of doughproducts, for example, the contents of the damaged starch kernels, whencooked, occur as losses in the cooking water and also give the cookingwater a milky-white color. But the same is also true in the productionof starch. The starch can only be separated from the gluten in aneconomical manner in that the protein bodies, which are alreadythread-shaped in themselves, are arranged to form a protein framework(gluten framework). This occurs by way of the formation of dough in thesame way as in dough products. The starch crystals can then float out ofthe protein framework by means of additional water and can be separated.In contrast, the baker wants the starch to be damaged in bread flour sothat the flour can quickly absorb much water for the formation of thebread dough.

The second finding consisted in keeping the number of grinding passesused for milling as low as possible, which allowed the initial costs forthe mill to be kept as low as possible. The solution corresponding tothese two findings is described in the present Applicant's DE-PS No. 2642 628. Ten to twelve grinding passes are used in this prior art.

DISCLOSURE OF INVENTION

The object of the invention is to achieve a further reduction of thecapital expenditure for a starch mill, but while ensuring the productquality, particularly the fractions required for the starch factory,especially the heavy fractions containing the A-starch, but also thetotal starch containing A- and B-starches.

The solution, according to the invention, is characterized in that thematerial is guided one to five times via double-grinding stages withoutsifting between the double grindings and is sifted subsequent to thedouble grinding in each instance.

In a manner which surprised those skilled in the art, this object wasmet in its entirety and the precondition was simultaneously created foranother stage of development for the preparation of raw material forobtaining starch. In this connection it was necessary to departcompletely from the traditional approach to milling practice of previousadvanced milling. It is still true that the grinding must be carried outwith extreme care and, accordingly, in multiple stages in order toachieve the maximum results with respect to all conventional milledproducts: opening the kernel, detaching the endosperm portions,carefully grinding the coarse semolina portions, production of thenecessary fine fractions without damaging the starch, etc. While thegrinding stages in themselves are not omitted, a part of theintermediate sifting can nevertheless be dispensed with by means of theconstruction of specialized mills--and this has now been shown by themost recent findings--without resulting thereby in a reduction in thequality and output of the fractions required for the production ofstarch, and this can be done with the same total throughput through themill. This means that the grinding is still effected in many stages andvery carefully.

The omission of a substantial part of the intermediate sifting (almosthalf) economizes on all the conveying elements previously required fortransportation, filters, etc., so that a mill becomes substantiallycheaper when the inventive idea is applied consistently. In particular,the operation of a mill, according to the invention, is made moreeconomical by means of reducing the devices to be serviced and by meansof reducing the conveying and drive energy. In addition, the reductionof the building volume can bring about noticeable savings.

The new invention allows various particularly advantageousconstructions.

It is especially preferable that the material undergo a double grindingtwo to four times, especially four times. This means the use of eightgrinding-roll pairs, which can consist of coarse and fine corrugationand smooth rolls, as customary in known advanced milling. The actualsifting passes are likewise reduced to four, which signifies a reductionof the sifting passes to 40 to 50% compared with the prior art.

However, depending on the raw materials used for grinding, particularlywith material which is more difficult to process, it may be advantageousto provide three to five single grindings for reduction with anintermediate sifting in each instance. Of course, this can be effectedin such a way that the corresponding roll mills are installed but onlyput into operation when needed, so that every unnecessary "handling" ofthe material is avoided and the maximum in careful treatment is ensuredin every case.

In addition, it is suggested that the material undergo double grindingat least at B₁ /B₂, B₃ B₄, C₁ /C₂ and C₃ /C₄.

The new invention is also directed to a starch milling system for theproduction of starch raw material from wheat, rye, corn or barley forsubsequently obtaining pure starch and is characterized in that itcomprises one to five double-grinding passes with two grinding-rollpairs arranged one after the other in each instance.

The new invention accordingly allows not only an enormous reduction interms of process technology, but also an effective reduction of therequired machinery and accordingly the overall construction volume. Butin this way an unexpected advance was achieved for the construction andoperation of starch milling systems.

In addition, the new solution enables, e.g. for the conversion ofexisting starch mills, the use of three to five of the previouslyutilized four-roll mills (that is, six to ten roll pairs), wherein twogrinding passes without intermediate sifting are connected one directlyafter the other. However, it is advisable to arrange all roll millsdirectly adjacent to one another on the same base without offsetting.

On the other hand, it is substantially more advantageous for new systemsthat the mill comprise one or preferably two eight-roll mills (rollmills with eight rolls) with two sets of grinding-roll pairs located oneon top of the other. Large starch mills are expanded simply by means ofcorresponding parallel operation of the work machines, that is, e.g.twice the quantity of units for twice the throughput capacity.

As can be seen, milling for starch milling systems accordingly reaches apoint where the state of the very old flat milling is reached again withrespect to the units which are used (two to three grinding passes), butwhere virtually all the advantages of advanced milling can be retained.

In addition, the new invention enables a whole range of particularlyadvantageous constructions and a considerable number of variations.Thus, it is possible to apply only double grindings in a consistentmanner without intermediate sifting between the individual doublegrindings. This results in a very concentrated production sequence.However, in difficult cases it is also possible to provide e.g. one tofive single grindings with an intermediate sifting in each instance forthe size reduction grinding. This has the advantage that a very highoutput and purity of the end product can be achieved even with kernelmixtures which are difficult to grind.

Approximately fifteen single passes is state of the art in present-dayflour mills, approximately ten to twelve single passes in starch mills.According to the new invention, it is possible to make due with four tofive double-grinding passes, that is, a total of eight to ten grindingpasses, but eight grinding passes, that is, two eight-roll mechanisms,is especially preferable. It can be seen that the number of roll pairshas been reduced, but particularly the "handling" such as sifting,transportation, etc. has been cut almost in half.

A small mill can accordingly be built with two, possibly threeeight-roll mills which comprise two sets of two grinding-roll pairs,which are located one on top of the other, or can be equipped, forexample, with two eight-roll mills and one or two four-roll mills.

Every grinding-roll pair preferably comprises its own grinding gapadjustment in each instance, so that the manner of operation of thegrinding rolls per se is only changed to a limited extent with respectto input on the part of the miller as compared with DE-PS 2 640 628, forexample.

In addition, it is suggested in eight-roll mills that the roll pairslocated on top comprise an adjustable feed regulating device in eachinstance, as well as a funnel-shaped product guide for directlytransferring from the respective roll pair located on top to the lowerroll pair.

Since expert management of a mill is also important with the newinvention, the miller in charge will likewise have correspondingopportunities for monitoring and influencing just as before. Therefore,a grinding gap adjusting device and also a control gate for removal ofsamples after every grinding pass are assigned to every roll pair. Therequirement that milling remain an art, in somewhat the same manner ascooking, is accordingly ensured.

For the purpose of reliable operation, the feed space of the upper rollpair and the feed space of the lower roll pair are connected to anaspirating device via ducts in the eight-roll mechanisms, particularlyin the area of the grinding gap. This also allows a high throughputcapacity and stable grinding conditions.

In addition, every roll pair is to be completely equipped withindividual adjusting devices and devices for protection against foreignbodies, and the rolls of every roll pair preferably have differentrotating speeds, wherein a jointly controlled moving-out device is to beassigned to the roll pairs located one on top of the other.

It is especially preferable that the rolls of a roll pair be arranged onthe same horizontal plane.

In a further development of the inventive idea, it is especiallypreferable that a plansifter with a large individual screening surface,a so-called large plansifter, be used which has a screening surfacewhich is approximately 30 to 60%, preferably 40 to 50% larger comparedwith the known plansifter screens which are presently used for the4-roll mills. As a result, a mill having a daily processing capacity ofapproximately 100 to 200 tons comprises, e.g. two eight-roll mechanismsand a single large plansifter. In addition to this, a compact cleaningapparatus, according to the CH-PA No. 04 626/87-6 of the presentApplicant, is used for cleaning, so that a compact starch mill isactually formed thereby which in principle has all the substantialadvantages of the previous starch mills but also an unexpected reductionin the number of required units and the required space. The entirecontents of the CH-PA No. 04 626/87-6 is an integral part of the newsolution according to the invention.

A basic unit of a starch mill with corresponding daily capacitycomprises a compact cleaning apparatus, two eight-roll mills and a largeplansifter.

For optimum management of a new starch mill, the grinding gap adjustingdevices are assigned in each instance to a remote control and computermeans are provided for storing and retrieving the specific grinding gapadjustments for all grinding tasks as well as all remaining adjustingvalues of the processing and transporting means.

If the raw material or mixture, respectively, is known, as well as therest of the parameters such as ambient temperature, air humidity, thestate of all units (corrugation of the rolls, screening tension of theplansifters, etc.), the mill can be operated completely automaticallyover a longer period of time, even without the immediate presence oftrained personnel, after a onetime accurate adjustment.

The invention is explained in more detail in the following.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an eight-roll mill,

FIG. 2 shows a view of half of FIG. 1 with the adjusting means anddrive,

FIG. 3 shows a new starch mill,

FIG. 4 shows the grinding and sifting unit and

FIG. 5 shows the new grinding process in a diagrammatic manner.

MODES FOR CARRYING OUT THE INVENTION

Reference is now made to FIG. 1. The eight-roll mill 1 comprises twohalves, the left half is shown as a bruising pass 2 and the right halfis shown as a second reduction pass 3. The bruising passes 2 comprise atleast corrugated rolls 4 and 5, respectively, wherein the roll 5 whichruns more rapidly is designated in the drawing with two arrows. A wipingbrush 6 is located below each roll 4 and 5. Rolls 7 and 8, respectively,which are smooth for the most part, are used in the second reductionpasses and wiping blades 9 are used for keeping the surface of the rollsclean. Depending on the specific grinding operation, the respectivelower roll pair 4', 5' or 7', 8', respectively, will be the same rolltype, coarse corrugation, fine corrugation, or will be constructed as asmooth roll, as the corresponding upper roll.

The material is guided to the left or to the right into the roll mill 1via a feed cylinder 10. Only in very large milling capacities is itindicated to construct the left-hand and right-hand roll mill halvesidentically in such a way that each half must process one half of theproduct volume. In the drawing, a sensor 11 in the feed cylinder 10 isdesigned as a so-called "Christmas tree" which controls a product feed12, so that an arriving quantity of material which flows into the feedcylinder 10 at the top is discharged in the same magnitude by means ofthe product feed. The material is guided directly into the grinding gapvia a feed duct 13. A strong air current is generated in the feed duct13, which can be ensured in an advantageous manner by means of two airducts 14 which are guided around the rolls 4, 5 and 7, 8, respectively.The material which is bruised by the upper roll pair 4, 5 is guideddirectly into the grinding gap of the lower roll pair 4', 5' via aproduct outlet funnel 21. The air is also aspirated through the airducts 14 at the lower roll pair 4', 5'. A transfer unit transfers thematerial to be milled to the intermediate lift-overs by means of aproduct outlet funnel 21. All four roll pairs 4, 5 - 4', 5'-7, 8-7', 8'can be adjusted with respect to the grinding gap by means of anadjusting device 15. All other devices, such as the means for protectingagainst foreign bodies, the engaging and disengaging device, etc. areused in the same manner as in standard four-roll mills. In thisconnection, reference is made to DE-PS No. 27 30 166 in its entirety. Ithas been shown that the constructional unit for the roll pair which isshown in the aforementioned publication of the present Applicant canalso be used to great advantage with the eight-roll mills, so that wheneight-roll mills are combined with four-roll mills the same basicconstruction of the so-called roll package can be taken as a basis inevery case, which is an additional advantage for both the manufacturerand the user.

In individual cases, it can be indicated to provide a feed roll orproduct distribution roll, respectively, above the lower roll pair.However, it is preferable that the engagement and disengagement of theroll be effected for both roll pairs by means of the same sensor 11.

The right half of the drawing also shows a product and air path 18 inthe product outlet funnel 21. This can be advantageous particularly withmilling materials of the middlings and flour types, since, in this way,a more compact guiding of the falling stream of material is madepossible by means of separate air and product paths.

Every grinding-roll pair (4, 5 - 7, 8) comprises its own grinding gapadjusting device which consists of a handwheel 15 and the correspondingadjusting elements. In addition, a motor-driven adjusting device 16 canbe provided, wherein both can monitor the instantaneous distancevariable between the two grinding rolls via a display 17. Moreover, themotor-driven adjustment can be effected automatically by means ofcomputers (R) and storage means.

In addition, a control gate 19, which is shown in the right half of thedrawing in the closed position at the top and in the opened position atthe bottom, is assigned to each grinding-roll pair. The control gate canbe opened regardless of whether or not the roll mill is operating.Constant air pressure conditions and, accordingly, constant grindingconditions, are thereby maintained by means of the additional air ducts14, 18 described above.

Reference is made in the following to FIG. 2 which shows adjustingmembers as a first constructional assembly 100 and a controllableadjusting drive as second constructional assembly 100'. The two grindingrolls 104 and 105 are supported on a mutual carrier 101. The movableroll 105 is fastened at a stationary eccentric pin 102 so as to beswivelable, wherein the inward and outward movement is controlled bymeans of a corresponding lever 103, as well as a disengagement cylinder106. The eccentric pin 102 is rotated by means of the swiveling movementof the lever 103 and causes a horizontal displacement of the lowerportion of the swivelable bearing housing 107, so that the spacing ofthe two grinding rolls can be roughly adjusted. This device would be tooinexact for an accurate adjustment of the grinding rolls. Also, this isonly used for bringing the grinding rolls into a moved-in or moved-outposition or into two fixed positions. The actual fine adjustment of thegrinding rolls 104 and 105 is effected via an adjusting spindle 108which directly moves an adjusting arm 109 around a stationary pivotbearing 110 by means of rotation. The upper, shorter end of theadjusting arm 109 is connected with the swivelable bearing housing 107in a force-locking manner via a tie rod 111. The transmission of forceis effected via knife edges which are part of an overload springprotection device 112 on one side. On the opposite side, an adjustablepressure head 113, as well as a pressure measuring device 114 withpressure display apparatus 115, are arranged at the tie rod 111. Inorder to be able to adjust the grinding rolls in a parallel mannerduring servicing operations, a correction can be effected on therespective necessary side via adjusting screws 143, 144. The adjustingspindle 108 is held so as to be stationary by means of the bearing 110'and can now be actuated via a handwheel 116, which has a display clockdirectly built into it, or by means of motor power, transmission chain118 and a gear motor or drive motor 119, respectively. The drive motor119 is fastened at the roll mill 126 and communicates directly with theadjusting spindle 108 via a slip clutch and a chain wheel.

In addition, a position indicator 120 is directly connected with thetransmission chain 118, so that every movement of the chain wheel 123 isrecorded in the position indicator 120 and guided further to the desiredposition. In FIG. 2, in addition, a drive belt 128 for the drive of thegrinding rolls 104 and 105, 104' and 105' respectively, is only shown ina suggestive manner. It is possible also to provide an electric powerrequirement measuring and display device 129 in the drive system. Theelectric power consumption can accordingly be defined at a lower andupper value, for example, and e.g. the grinding rolls can be moved apartwhen the preselected range is exceeded.

All signals of a roll mill are preferably coordinated and controlled viaa machine computer, wherein the machine computer can request thenecessary desired values from a central computer with storage. Theposition indicator is preferably equipped with a position limiting valueswitch which is adjustable to preselectable limiting values and canimpede an automatic faulty adjustment in this way. The position limitingvalue switch in the position shown has the advantage that a faultymanual adjustment can also be prevented accordingly, since both thehandwheel and the automatic adjustment result in a correspondingdistance displacement of the chain 118. In the same way as the adjustingmotor 119, the position indicator can be connected with an input-outputdevice which receives and transmits corresponding signals from themachine computer, corresponding to the digital display and manual inputkeys. In the same way, the pressure measuring and display device 114,115 can be connected to the machine computer. Depending on the degree towhich a roll mill can be expanded, one or more protection devices can beprovided at the same roll mill. If, for example, corrugated rolls areinstalled, monitoring of the grinding pressure is less important; on theother hand, the monitoring of the spacing of the grinding rolls, whetherthis be effected by means of the position indicator or a distancemeasuring device, is advantageous. The opposite applies to smooth rollsin which a monitoring of pressure is more advantageous. A computer andthe signal lines, which are indicated in a suggestive manner, aresupposed to indicate that the computer and memory, respectively, controlan entire range of roll mills in a mill, possibly all of them, and, ifnecessary, also coordinate control functions.

In addition, it has proven to be especially advantageous that thedigital display transmit a value corresponding to a time measurement(clock 05:50) and preferably transmits an identical value correspondingto a position indicating apparatus or display clock of the handwheel,respectively.

The great advantage consists in that the experimental values of rollmills which are not automated and not remotecontrollable are comparedand can be evaluated for constructing or improving corresponding controlprograms.

FIG. 3 shows a complete starch mill in a greatly simplified manner.Roughly considered, the starch mill consists of a storage silo 30 forthe stored grain, mixing and holding boxes 31, an actual processing wing32, and finished product cells 33. Subsequent to the finished productcells 33, the starch fraction is transferred directly to the starchfactory via transporting elements 34.

In particular, the work sequence proceeds as follows: The desiredmixture of raw grain is provided from storage cells 35, 35₁, 35₂, 35₃,etc. and conveyed into mixing cells 40 via trolleys 36, a horizontalconveyor 37, an elevator 38, and another horizontal conveyor 39. Thegrain, which has still not been cleaned, is removed from the mixing cell40 and conveyed into the grain cleaner 44 via scales 41, a horizontalconveyor 42 and an elevator 43. Large extraneous constituents(scalpings) are sifted out, stones are sorted out and hull parts areaspirated away in a compact cleaning apparatus. (Reference is made toCH-PA No. 04 626/87-6 of the present Applicant in its entirety.)Subsequently, the material is delivered to a trieur 45, in which longand round extraneous seed materials are removed, dirt adhering to thekernel material is removed by means of a scouring machine 46, therequired quantity of water is added in an intensive wetting device 47and the material is stored in a holding cell 48 for the necessary periodof time. The grain, which has been wetted and let stand forapproximately 12 to 48 hours, is removed from one of the holding cells48, 49 and 50, respectively, lifted over by means of an elevator 43'and, after the addition of 0.1 to 0.3% water (wetting 51 before B₁) anda homogenization cell 52, is fed directly to the first grinding pass(B₁) or the first double-grinding pass 53, respectively. After fourdouble grindings 53, 53', 54, 54' and a (total of four) sifting passes,the fractions obtained are guided away via a pneumatic conveying system55, bran is stored in a storage silo 56, and the starch fraction isstored in one of the storage silos 57, 57' or 57". After a subsequentweighing (scale 60), the material is conveyed into the starch factory bymeans of the transporting elements 34. The entire system control meansand locking mechanism, as well as the computer means 58, areaccommodated in a control room 59.

FIG. 4 shows the actual core of the starch mill, wherein the grindingand sifting passes are shown in an enlarged manner. This is a modulehaving a milling capacity of 100 to 200 tons daily output. Twoeight-roll mills 70 and 71, respectively, and a large plansifter 72 arerequired for this. The first eight-roll mill 70 contains the grindingpasses B₁ and B₂ as first double pass and B₃, B₄ as a second doublepass. The second eight-roll mill contains grinding passes C₁, C₂ as afirst double pass and C₃, C₄ as a second double pass, that is, a totalof four double-grinding passes. The plansifter 72 constitutes in itselfa single oscillating unit. Four sifting divisions 73, 74, 75, 76 areshown which are arranged vertically one on top of the other, wherein theproduct streams are only shown in a very schematic manner. But, theplansifter can comprise completely different gradations, that is, alsosix or eight vertically arranged sifting divisions. Every verticalsifting division can be divided two or more times in height, whetherthis is for double streams or for another guiding of the productcorresponding to an optimization of the utilization of the sifters. Alsoshown only in a schematic manner is the first influx 61 of ungroundgrain material at B₁, intermediate liftovers 62, 63, 64, 65 and theconveying system with the good starch fraction which is shown by arrow55 pointing outward.

FIG. 5 shows a milling process diagram shown in a manner similar to thesolution of the prior art shown in DE-PS 26 42 628. As can be seen, boththe number of sifting passes and the number of grinding passes have nowbeen drastically reduced. However, the four bran brushes 80 forincreasing the output of endosperm fractions remain.

The prepared raw grain (e.g. wheat) is fed to the first grinding-rollpair B₁. The first bruised grain and broken up grain, respectively,produced by B₁ proceeds directly to the second grinding-roll pair, toB₂, without sifting between B₁ and B₂. After the second grinding, theso-called second bruised grain obtained is guided to the first siftingdivision 73. The second bruised grain is divided up into differentgranulations by the plansifting of the sifting division 73, wherein thefraction intended for B₃ is temporarily guided via a Br.₁ to a firstbran brush (80) and the tailings are then directly transferred into thethird grinding B₃. The material, which is still in the form of bruisedgrain, is ground by means of B₃ and ground by means of B₄ directlyafterward. The B₄ bruised grain, which is now produced in the seconddouble grinding, proceeds to the second sifting division 74, wherein thematerial is again divided up into a plurality of granulations.

A portion of the fraction from the first and second sifting passes isgiven to dividers Div. 1, Div. 2 which produce a still finergranulation.

The coarse tailings from both the first and second sifting passes (fromsifting divisions 73 and 74) are guided to the corresponding branbrushes 80 (Br.₁, Br.₂, Br.₃, Br.₄) depending on the respective givenconditions. The tailings from the divider (Div. 1) proceed directly tothe first reduction passes R₁ (C₁). From there, the material is againguided directly to the second reduction pass R₂ (C₂) withoutintermediate sifting, and the product which is reduced by means of R₂ isgiven directly to a third sifting division 75.

The semolina or middlings resulting in the third sifting pass is thengiven to the fourth reduction pass P₁ (C₃) and, right after this, thesecond stage of the same reduction pass P₂ (C₄), and the resultingrefined middlings are given to the fourth sifting division 76. Thetailings of the fourth sifting pass 76 are additionally crushed in animpact mill E₁ and guided directly to the following sifting division.

The finest fraction (the lowest siftings), as well as the lowestsiftings of all remaining sifting portions proceeds from the siftingdivisions into the intermediate storage 57 to 57" as finished productand is ready for processing in the starch mill.

It can be advantageous to insert a detacher (for detachingflakes)--designated in a symbolic manner with a circle and cone--betweenthe reduction double passes R₁ - R₂ and P₁ - P₂, respectively, and thecorresponding sifting division 75 and 76, respectively.

We claim:
 1. In a method for the production of a starch raw material forsubsequently obtaining pure starch from wheat, rye, corn or barley,wherein fractions of the starch raw material which are damaged as littleas possible are produced by means of roll grinding and sifting devices,wherein the material is ground repeatedly and sifted with a system ofadvanced milling, the improvement comprising the steps of: guiding thematerial two times via double-grinding stages wherein eachdouble-grinding stage comprises a first and second grinding and thematerial is ground without sifting between the first and secondgrindings and sifting the ground material following the second grinding.2. A method for the production of a starch raw material for subsequentlyobtaining pure starch from wheat, rye, corn or barley, wherein fractionsof the starch raw material which are damaged as little as possible areproduced by means of roll grinding and sifting devices, wherein thematerial is ground repeatedly and sifted with a system of advancedmilling, the improvement comprising the steps of: guiding the materialfour times via double-grinding stages wherein each double-grinding stagecomprises a first and second grinding and the material is ground withoutsifting between the first and second grindings and sifting the groundmaterial following the second grinding.
 3. A method according to claim1, wherein three to five single grindings are carried out in combinationwith the double grindings with an intermediate sifting in each instanceparticularly for size reduction.
 4. A method according to claim 2,wherein the material undergoes double grinding at least at bruisingstages B1/B2, B3/B4, and reduction stages C1/C2 and C3/C4.
 5. In astarch milling system for the production of starch raw material fromwheat, rye, corn or barley for subsequently obtaining pure starch, theimprovement comprising two double grinding passes, each pass comprisingtwo grinding-roll pairs arranged so that the grind output of one pairdirectly forms the input of the next pair without sifting therebetween,thereby defining a double-grinding pass, said grinding passes being partof an eight roll roller mill with two sets of grinding roll pairsarranged one above the other.
 6. A starch milling system according toclaim 5, wherein the system comprises at least one eight-roll rollermill, each eight-roll roller mill with two sets of two grinding-rollpairs which are arranged one above the other.
 7. A starch milling systemaccording to claim 5, wherein each of the grinding-rolls pairs has itsown grinding gap adjustment.
 8. A starch milling system according toclaim 6, wherein, in the eight-roll roller mills, an adjustable feedregulating device is assigned to the roll pair located on top in theeight-roll roller mills, and a funnel-shaped product guide is arrangedbetween the roll pair located on top and the roll pair located at thebottom for directly transferring from the roll pair located on top tothe roll pair located at the bottom.
 9. A starch mill according to claim5, grinding gap adjusting devices and a control gate for removingsamples after every grinding pass are assigned to each roll pair.
 10. Astarch milling system according to claim 5, wherein each roll pair has afeed space and a grinding gap and the feed space of the upper roll pairas well as the feed space of the lower roll pair and the grinding gap ofthe lower roll pair are connected to an aspirating arrangement viaducts.
 11. A starch milling system according to claim 5, wherein everyroll pair is completely equipped with an individual adjusting device, aswell as a device for protection against foreign bodies, and the rolls ofeach pair have different rotating speeds, wherein the roll pairs locatedone on the top of the other include a moving-out device which iscontrolled jointly.
 12. A starch milling system according to claim 5,wherein the rolls of each roll pair are arranged in the same horizontalplane.
 13. A starch milling system according to claim 5, wherein itcomprises a compact cleaning apparatus, at least two eight-roll rollermills and a large plansifter.
 14. A starch milling system according toclaim 6, wherein the grinding gap adjusting device is assigned in eachinstance to a remote control and computer means for storing andretrieving the specific grinding gap settings for every grinding task,as well as all other adjusting values of processing and transportingmeans.